Generators for producing energy work by collecting and converting kinetic energy created through mechanical means such as a spinning action. Windmills are an example. There have also been attempts to generate energy based on the movement of vehicles.
One type of device for electricity generation in motor vehicles makes use of a ground engagement wheel. For instance, U.S. Pat. No. 5,921,334 Al Dokhi claims a ground dragging wheel on the undercarriage of a vehicle connected to a pulley operating to spin the shaft of a generator. This configuration requires movement of the vehicle in order to produce energy. U.S. Pat. No. 5,680,907 to Weihe discloses a similar ground engagement wheel as Al-Dokhi except that the ground engagement wheel is used simply as a gear to move the vehicle wheel, not for producing energy (the wheel is itself powered by solar panels on the roof of the vehicle claimed).
Another example of electrical generation from vehicles is regenerative braking. These systems only create energy while braking or going downhill.